Elevators are presently provided with a plurality of braking devices. In normal operation, the brakes hold the elevator car in place where it stops at a landing. In emergency situations, the brakes may stop the elevator car from plunging into the hoistway pit.
One known braking device for emergency motion is a governor triggered braking device. The governor triggered braking device comprises a governor, a governor sheave assembly, at least one safety, and a governor rope.
The governor is a mechanical speed control which monitors the speed of the elevator car; a centrifugal force means is used for detecting the overspeeding elevator car.
The governor sheave assembly comprises a governor sheave at the top of the hoistway and a tension sheave at the bottom of the hoistway which guide the governor rope and keep tension on it.
The safety is a mechanical device attached to the elevator car frame employed to stop and hold the elevator car in case of predetermined overspeed or free fall. The governor triggered braking device operates as follows.
The governor rope is looped over the governor sheave at the top of the hoistway and the tension sheave at the bottom of the hoistway and is attached to the elevator car. As the governor rope exceeds the rated speed of the elevator car by a limit, the governor grabs the governor rope which pulls on a linkage attached to the elevator car, thereby triggering one or more safeties. This brakes the elevator car.
Elimination of the governor braking device would reduce the amount of machine room and pit equipment which in turn would reduce installation and maintenance costs.